Trap loss of spin-polarized 4 He* & He* Feshbach resonances Joe Borbely ( ) Rob van Rooij, Steven Knoop, Wim Vassen

Trap loss equation Experimental details: – Setup – Procedure Results with 4 He* – magnetic-field dependent trap loss rates Present work – Feshbach resonance: 3 He*- 4 He* Bose-Fermi quantum gas Outline

Trap loss equation Experimental details: – Setup – Procedure Results with 4 He* – magnetic-field dependent trap loss rates Present work – Feshbach resonance: 3 He*- 4 He* Bose-Fermi quantum gas Outline

Trap loss equation He*: eV In a spin-polarized gas, Penning ionization is forbidden due to spin conservation. Total spin of the colliding particles in the final state cannot exceed 1, whereas initially the total spin is 2 In an unpolarized gas two-body losses yield, Time evolution of trapped density, L 1 : background (one-body) collisions L 2 : two-body collisions In spin-polarized He* PI suppressed by 10 4 → one reason for achieving BEC L 3 : three-body collisions: very large release energy Dominant

However, our detection signal (the MCP) is a measure of atom number, not density We are interested in solving c 2 and c 3 are constants that depend on trap geometry Trap loss equation Axial frequencyRadial frequency time (ms)

1. Collisions with background gas Trap loss equation metastable helium can ionize all atoms (through collisions) - except neon (and ground state helium) atoms

2. The spin-dipole interaction induces two inelastic two-body (L 2 ) collision processes: - Relaxation Induced Penning Ionization (RIPI) - Spin Relaxation (SR) GV Shylapnikov et al, PRL 73, 3247 (1994) PO Fedichev et al, PRA 53, 1447 (1996) V Venturi et al, PRA 60, 4635 (1999) couples Dominate loss mechanism Trap loss equation

3. Recombination can occur due to interaction between spin-polarized 4 He* in the course of three-body collisions (L 3 ) Two-body Penning Ionization spin-polarized helium molecule two-body PI 4 mK >> 1  K Trap loss equation

Experimental details: – Setup – Procedure Results with 4 He* – magnetic-field dependent trap loss rates Present work – Feshbach resonance: 3 He*- 4 He* Bose-Fermi quantum gas Outline

electron bombardment eV 1557 nm 2059 nm 1083 nm 2x ~120 nm 1557 nm laser light 1083 nm laser light MCP Same laser but different frequency detunings for: collimation slowing cooling trapping detection Experimental setup

magnetic field ~100% tranfer magnetic field atom+photon energy Dressed picture of 4 He* in an RF field Experimental Procedure Atoms are confined in the dipole trap Both m=+1 and m=-1 magnetic substates are trappable

Trap loss equation Experimental details: – Setup – Procedure Results with 4 He* – magnetic-field dependent trap loss rates Present work – Feshbach resonance: 3 He*- 4 He* Bose-Fermi quantum gas Outline

One-body loss: L 1 Atomic transfer: BEC thermal assumption: thermal equilibrium holds during one-body decay of a condensate loss of a thermal atom (i.e. collisions with background gas) cause a free place in the otherwise saturated thermal distribution a BEC atom fills the thermal hole (keeps thermal equilibrium) Theory: Experiment: (a) (b) 1.7(2) 1.5(2) 80% - 20% 50% - 50% BEC% - Thermal% long times (> 15 sec)

Three-body loss: L 3 Fix:  Magnetic-field independent  Identical for m=+1 and m=-1 atoms s  Use only m=-1 atoms (since L 2 =0) AS Tychkov et al, PRA 73, (R) (2006) Present result: VU previous result: Seidelin result (modified): S Seidelin et al, PRL 93, (2004)

Two-body loss rate: L 2 Fix:

Two-body loss rate: L 2 N ms N 2 s

Two-body loss rate: L 2 (Comparison with Theory)

Trap loss equation Experimental details: – Setup – Procedure Results with 4 He* – magnetic-field dependent trap loss rates Present work – Feshbach resonance: 3 He*- 4 He* Bose-Fermi quantum gas Outline

Energy Atomic separation, R Feshbach resonance 0 two free atoms entrance channel U bg (R) U bg (R) asymptotically connects to two free atoms in the ultracold gas U b (R) can support molecular bound states near the threshold of the entrance channel Feshbach resonances are a tool to control the interaction strength between atoms (ultracold chemistry - He*Rb Efimov physics - Steven Knoop) In the ultracold domain, collisions take place with atoms that have nearly zero energy scattering length B 0 quintet molecular bound channel singlet U b (R) Zeeman energy of the atomic scattering state becomes equal to that of a molecular bound state because of the difference in magnetic moments coupling EcEc  B What is a Feshbach resonance?

Feshbach resonances in He*   ~1  s B 0 = 99 G  B=2 mG  1 <<  5

21 Feshbach resonance in 3 He*- 4 He* smsms magnetic trap 3 He*(2 3 S f=3/2, m f =-1/2) 4 He*(2 3 S f=1, m f =-1) b A 3He*(23S f=3/2, mf=-3/2) a Dipole trap

RF spectroscopy 3 He*- 4 He* Feshbach resonance Feshbach resonance in 3 He*- 4 He* 3 He*(2 3 S f=3/2, m f =-1/2) + 4 He*(2 3 S f=1, m f =-1) b: 3 He* m f =-1/2 A: 4 He* m f =-1 a: 3 He* m f =-3/2 Energy difference: A+b - Ab Threshold = A+b energy Enhanced trap loss at FR Get information of triplet molecular state RF A+bA+b AbAb A+a no collisions between identical fermions limited by three-body loss rate

Questions?